Here's a good explanation for those who insist the US doesn't have a blockade on Cuba:

Last edited Sun May 4, 2014, 04:41 AM - Edit history (1)

From The US Blockade of Cuba: Its Effects and Global Consequences
Nicholas Partyka I Geopolitics I Analysis I May 2nd, 2014

~snip~

In the US, this set of economic warfare policies is commonly called the embargo against Cuba. In the rest of the world, and especially in Cuba itself, this same set of policies is called the US blockade of Cuba. This is not simply a semantic quibble. The US specifically chooses to label its policies an embargo to avoid the moral (as well as legal) complications involved in a blockade. The same kind of geo-strategic (as well as domestic policy) considerations go into deciding whether or a nation has a "civil war" or mere "sectarian conflict". If one looks to technical definitions, an embargo is a full or partial prohibition of trade with a particular country imposed by another country. A blockade, on the other hand, is an attempt to prevent food, medicine, and or other kinds of war materials from entering a particular country. In this light, the US has a policy both of embargo and blockade.

From the point of view of international law, the US blockade policy is illegal. The terms of the so-called embargo run entirely contrary to explicitly stated clauses of several of the most foundational documents establishing modern international legal norms. For much of the history of the US blockade, the US government has prohibited sales of food and medicine to Cuba; this is expressly declared illegal in the Geneva Convention. It was only towards the end of the Clinton administration that the ban on US food exports to Cuba was partially lifted. The Bush administration tried to reverse this decision, but was not successful.

According to international law, a blockade is illegal in peace time. Unless war is declared between two nations, it is illegal for one to blockade the other. This much is made very clear in documents to which the US is signatory. That such a policy is illegal, or at least to be frowned upon, can also be seen in the legal wrangling that occurred within the US during the initial enforcement of the blockade. The only way President Kennedy was able to legally impose the provisions of the blockade policy in the first place was by invoking the Trading with the Enemy Act of 1917. This law allowed the government to prohibit US citizens from doing business with citizen or firms of nations with which the US is at war. The legal structure of the blockade policy applied to this law through a technicality. The Kennedy administration made use of the fact that the Korean War was not technically over, and so there was still a state of emergency in effect. The fighting in the Korean War was terminated with an Armistice, and not a Peace Treaty, and thus the two nations were still technically at war.

Rather strikingly, the voice of the international community is clear and highly united on its view of the blockade. Every year, for the last twenty years, the UN general assembly has voted to pass a resolution condemning the US blockade (not "embargo" mind you) of Cuba. For the majority of these two decades of votes, the outcome has been rather lopsided against the US. This is to the point now that, for many years in a row, 185 or more countries have voted to condemn the US blockade policy. The only nation consistently voting with the US is Israel. This should not be surprising since the Israelis are the only other nation in the world currently imposing a blockade on another nation, i.e. the Palestinians.

The blockade policy is not just enforced against Cuba, but it is also enforced against 'third-party' nations that trade with Cuba. For decades, each successive US administration has applied strong arm tactics to foreign governments, foreign firms and banks, and foreign subsidiaries of US firms and banks in order to get them to cease commercial relations with Cuba. Over the years, and continuing on today, this is a very expensive practice; both in terms of real money expended on enforcing compliance, etc., and in diplomatic capital. It is an accepted norm of international law that foreign-owned subsidiaries are subject to the law of the country that hosts them. This is seen as an important component of national sovereignty. It is thus perceived as an affront to the desired national sovereignty of many nations when the US government uses coercive methods to impose compliance with its blockade policy on those governments, domestic firms and banks, and foreign-owned subsidiary firms and banks.

In one typical instance of how the US imposes its blockade on third parties, the US uses access to its markets in order to force foreign firms and US-owned subsidiaries to comply with its embargo. French and Italian firms that export metal goods to the US market must be able to prove to the Office of Foreign Assets Control (OFAC) that none of the items they want to import contain more than 10% of Cuban-made products. In the case of the metal suppliers this product is typically Cuban nickel. Cuba has rich nickel deposits, and in a different world, would make good money exporting this resource. Technically, these exporting firms are free to buy whatever inputs they desire, and no one is going to force them to buy from this supplier or that. However, in order to import the goods made with those raw materials, they must meet the conditions set forth - which each sovereign nation can lawfully impose - that the US dictates. So, if you are a metal products exporter in Europe, your choices are as follows: Buy Cuban nickel and try to prove to the satisfaction of the US that none of the things you're exporting to the US contain any of that Cuban nickel. Or, as is what usually happens, stop buying Cuban nickel, because if you don't use it in production, then the US won't give you a hard time when you try to export your products to the US market.